1. Field of the Invention
The present invention relates to a marine propulsion device.
2. Description of the Related Art
Outboard motors and other such marine propulsion devices include exhaust passages for discharging exhaust from the engine. A honeycomb structure composed of, for example, a catalyst carrier is disposed inside the exhaust passage. In a marine propulsion device, exhaust is discharged from the engine into the water via the exhaust passage. Because of this, it is possible that the honeycomb structure may become wet due to water infiltrating from the exhaust passage. Moreover, in cases where the honeycomb structure is retained within the exhaust passage via a retainer mat, the retainer mat deteriorates if it becomes wet. If the retainer mat deteriorates, retention of the honeycomb structure becomes looser, and the honeycomb structure can no longer be retained.
According to a catalytic converter disclosed in Japanese Laid-open Patent Application No. 2003-020939, a stopper is disposed downstream from the retainer mat of the catalyst carrier, and the catalyst carrier is prevented from shifting towards the downstream end by the stopper. However, because the stopper is extended inwardly in the radial direction past the outside peripheral face of the catalyst carrier, the flow channel cross section of the catalyst carrier is constricted. For this reason, the exhaust gas cleaning performance of the catalyst is diminished.
According to an exhaust gas treatment device disclosed in Japanese Laid-open Patent Application No. 2006-070886, there is provided a stopper portion which is spaced apart from the retaining mat, and which protrudes by a protrusion amount less than the thickness of the retainer mat. Consequently, in the event that the retainer mat and the catalyst carrier move in unison, the movement of the retainer mat and the catalyst carrier can be stopped by the stopper portion. Moreover, owing to the small protrusion amount of the stopper portion, constriction of the flow channel cross section of the catalyst carrier by the stopper portion is prevented.
However, with the exhaust gas treatment device disclosed in Japanese Laid-open Patent Application No. 2006-070886, in the event that only the catalyst carrier has moved, the catalyst carrier cannot be caught by the stopper portion. It is conceivable that in a marine propulsion device, the retainer mat may become wet and deteriorate due to water infiltrating from the exhaust passage in the manner discussed above. In such a case, with the stopper portion of Japanese Laid-open Patent Application No. 2006-070886, when the retaining power of the retainer mat declines owing to deterioration, the catalyst carrier may slip out from the retainer mat.